Things to do to improve the GK61 in very simple terms would be things like lubing the switches/stabilizers.
Switching to a nice keycap set would also be appreciated by your fingers.
If you wanna get DIY/DIWHYYY territory, you could line the bottom of your case for pennies to give it a premium heft for literally pennies.
You could vinyl wrap the plate for a colored accent that you’d catch between your keycaps. I’ve done this before and I think it can turn out quite nicely for a small aesthetic accent.
You could vinyl wrap or sticker bomb your case to give it a bit more of your own identity.